Justifying Artifacts for Rhetorical Analysis......

In preparing my term paper, I had to revisit a question that I have encountered previously in my studies in TCR. How to justify the number and types of artifacts that are used for rhetorical analysis? We have read important, singular works by rhetoricians, philosophers and other scholars. Great detail was devoted to analyzing what the author's intent may have been. But in transferring classical rhetorical strategies to contemporary examples, what constitutes a valid artifact? In my paper, for example, I explore the different 'arrangement' or scientific information presented to an audience of students (via a textbook) and an audience of the general public (via a TEDtalk). To justify my use of the specific artifacts, I quoted the number of views for the TEDtalk and a publisher's ranking of the textbook. Is this valid? What are your thoughts? What strategies have you all used to justify the importance or value in a particular artifact or set of artifacts?